The research, conducted by Willaim Frey of the University and his colleagues in Germany, shows promise for other drugs that don't usually penetrate the blood-brain barrier, according to the U.S. News and World Report story. If the cells are suspended in fluid, they quickly reach the brain fully intact. The research was recently published in the European Journal of Cell Biology.

How did they conduct the research? Having mice sniff dropped of adult rat stem cells. Sounds like a task in itself.More from U.S. News and World Report:

An hour later, rat stem cells were clearly visible in the mice's brains. To make sure the ability to penetrate the brain wasn't limited just to those cells, they also had rats snort a second type of cells, from human brain tumors. These cells also penetrated the brain within an hour.

They likely traveled to the brain along the olfactory (smell) nerves through small holes in the cribriform plate, a thin horizontal part of the skull at the base of the brain. They also likely traveled inside fluid-filled spaces that surround blood vessels passing from the nose to the brain.

Just above the cribriform plate, olfactory nerves connect to the olfactory bulbs, two round extensions of the brain that process smell. Stem cells were found in the olfactory bulbs and also in the cerebral cortex, cerebellum, and other brain regions.

Stem cell treatments for brain disorders aren't approved yet by the Food and Drug Administration, but researchers hope this easy-to-administer method could help advance research into possible treatments for head injuries, stroke, Parkinson's disease, Alzheimer's disease, and Huntington's disease.